The present invention relates generally to the treatment of process materials such as municipal waste material. More particularly, the present invention pertains to an apparatus, system and method for treating process materials that have already been subjected to preliminary processing in a steam autoclave.
Landfills are commonly used to dispose of waste materials of many different types. These waste materials can include paper products, food scraps, yard waste, metal, glass, plastic and a host of other materials. In an attempt to reduce the amount of waste material that is deposited in landfills, source separating efforts in the form of recycling programs have been instituted. To the extent they are used, such recycling programs help reduce landfill dependence. However, it has been found that such recycling programs only result in the removal of a relatively small percentage of the total waste material. In the case of at least some material, such as paper products and other materials, the relatively small recovery rate can be attributed at least in part to the fact that a large percentage of the products are food-contaminated and thus quite difficult to separate and recycle.
In commonly assigned U.S. Patent Nos. 5,445,329 and 5,655,718, which are incorporated herein by reference, the disclosed apparatus, system and methods for treating processed materials are well suited for effectively and efficiently treating materials of many different types, including municipal solid waste. Organic and inorganic materials can be conditioned by varying treatment parameters, thereby facilitating sorting by size and density separation into their primary components. The subject matter disclosed in the above-referenced patents allows separation of food waste, ink, oil, grease and other related products from a host of base materials, such as metal, glass and paper. Food products, for example, can be solubilized and then extracted from the waste stream. Additionally, a relatively clean, high quality form of cellulose can be recovered from the waste stream. It is also possible to obtain clean metal products, which are much more readily acceptable as feedstock for various industries. Likewise, paper products can be treated to produce high quality recyclable material that can be separated for use in various industries. For example, through use of a fractionator, longer fibrous material can be divided out from the shorter fibrous material, with the former having possible use in the paper industry as recycled paper, and the latter being converted to a fuel, possibly for use in the electrical industry.
The methods, apparatus and system disclosed in the above-referenced patents use heat and pressure combined with moisture variation and controlled venting and tumbling in order to refine the quality of the resulting feedstocks that are produced from the municipal waste. Heat is added to the steam autoclaves disclosed in the above-referenced patents both by the addition of steam directly into contact with the waste materials within the autoclaves, as well as by the introduction of a heated fluid which is transported through the interior of the vessels within conduits in order to heat and/or dry the material located in the steam autoclaves. The heat and pressure within the steam autoclaves is increased such that the steam reaches a saturated state, and then after a predetermined time, the steam is rapidly vented in order to drop the pressure within the vessels quickly from a higher pressure to a negative pressure, thus reaching a superheated state and causing a release of enthalpy from the conditioned waste materials within the vessels. The biomass that results from the processes disclosed in the above-referenced patents can then be passed through screens, with the screened waste material from the steam autoclaves constituting approximately 70% of the total incoming waste stream when the screens are provided with approximately xc2xd inch openings. This fraction of the total incoming waste stream also includes approximately 95% of all the organic materials present in the municipal waste.
The present invention provides an apparatus, system and methods for treating the separated biomass that results from processing within the steam autoclaves disclosed in the above-referenced patents, although the invention also has useful application for treating materials resulting from different processing. The present invention further enhances the qualities of the separated biomass produced by the above-referenced steam autoclaves in order to optimize its use as a feedstock for a number of recycling and secondary industries. The end product produced by the methods, apparatus and system according to the present invention includes cellulose fibers that are readily recyclable for the paper industry, and/or useful for cellulosic insulation, a residual fine fiber fraction that can be used in compost as a soil amendment or used directly as a solid fuel, and biogas that is also useful as a fuel.
The present invention works synergistically with biomass produced by the methods and systems disclosed in the above-referenced patents as a result of the enhancements to the biomass for use by the recycling industry. Some of the significant enhancements to the biomass produced by the methods and systems according to the above-referenced patents are enhancements to the organic material that result from the pressurized cooking and solubilization of the organic materials that occurs within the steam autoclaves. The food wastes and other organic materials processed through the steam autoclave are largely solubilized and have an increased biodegradability when compared to fibers that have not been processed through the steam autoclave. The tumbling action of the steam autoclaves also results in finer particles than would result after an expenditure of the same amount of energy in a conventional hydro-pulping process currently used to pulp waste paper. Other enhancements to the biomass produced by the steam autoclaves include the dispersion of oils, suspension of lacquers and inks, solubilizing of coatings, and after some successive gravity and density separations and size screenings as well as dilution rinsing, the production of a clean ligno-cellulosic fiber that is very low in debris and suitable for incorporation within secondary fiber pulp used for paper manufacturing.
The cellulose fibers that are separated from the biomass produced by the steam autoclaves have also been shown to have a significantly higher freeness, or ability to rapidly drain water, when compared to conventional sources of fiber such as recycled old corrugated containers and ground wood fiber. The higher freeness as well as improved strength characteristics of the fibers separated by methods and apparatus according to the present invention significantly increases the value of these processed cellulose fibers to the paper making industry since energy requirements are reduced with the paper making machines being able to run faster.
The temperatures of between 260xc2x0 F. and 270xc2x0 F. that are reached within the steam autoclaves also have been found to enhance the characteristics of the cellulose fibers separated from the biomass produced by the autoclaves. Paper fiber generally includes lignin that binds to the cellulose fiber, hemicellulose, which is the soluble portion of the cellulose, and cellulose, which is basically very difficult to solubilize unless it is treated with acids, etc. Because the softening point of the lignin is approximately 262xc2x0 F., the temperatures reached within the steam autoclaves cause the lignin that binds to the cellulose fibers to be softened, but the lignin is not heated enough to be crystallized. Low melt point plastics within the biomass form into small beads that are easily separated during subsequent density and size separations so as to not be included with the cellulose fibers used by the paper industry.
In a method of treating waste material according to an embodiment of the invention, the waste material has first been subjected to increased temperature, pressure and mechanical shearing action in a steam autoclave to produce a biomass having at least one characteristic selected from a group of characteristics that are desirable in the recycling industries that use the various separated portions of the biomass. The enhanced characteristics of the separated portions of the biomass include the higher freeness or ability to rapidly drain water of the cellulose fibers that are provided to the paper recycling industry, good strength characteristics when compared to recycled corrugated cardboard containers and ground wood pulp, finer particle sizes than those that are achieved by conventional hydro-pulping of waste material for the same amount of energy consumed, aseptic properties, which result from the materials within the steam autoclave having been raised to high temperatures and pressures and then rapidly dropped to a negative pressure, the majority of the organic materials in the biomass being solubilized and the increased biodegradability of the cellulose fibers when compared to fibers that have not been autoclaved.
In a method, apparatus and system according to an embodiment of the present invention, the biomass having these enhanced characteristics can be subjected to separation processes wherein components of the biomass are separated by density, and/or size separation processes such as screening, wherein components are separated by size. A method according to an embodiment of the invention may also include the step of diluting the biomass with process water and subjecting the diluted mixture to a gentle mixing action, with the selected temperature and mixing action being effective to relax and straighten the cellulose fibers that have become twisted and tangled during the steam autoclave process. This latency removal step is used when the resulting cellulose fibers are to be further processed for use by the recycled paper industry.
In a method according to another embodiment of the invention, the biomass obtained from the steam autoclaves can be added to a sump or reservoir along with fluids obtained from a hybrid anaerobic digester that includes separate zones for biologically processing solids and fluids, to produce a solution with the proper ratio of solids to fluids for pumping and introduction to a gravity separation process such as in a liquid cyclone. The hybrid anaerobic digester allows for independent processing of solids and fluids, and therefore can provide all of the necessary fluids for operation of the liquid cyclone, thus working in an essentially closed loop with the liquid cyclone.
Additional processing of the biomass material and/or fine fiber fraction according to the invention can occur within a hybrid anaerobic digester, which is a vessel having separate zones for the biological processing of solid materials and fluid materials, with the processing of the fluid materials being independent from the processing of the solid materials. The vessel forming the hybrid anaerobic digester is preferably cylindrical with a conical bottom. The vessel has an outer wall that is cylindrically shaped over a portion of the height of the vessel, and conically shaped at the bottom portion of the vessel. A cylindrical intermediate wall is spaced inwardly from the outer wall, and a hydraulic reservoir is defined between the intermediate wall and the outer wall. An inner, cylindrical wall is spaced inwardly from the intermediate wall, with an attached growth media zone containing growth media defined between the inner wall and the intermediate wall. A lower portion of the inner wall is perforated to provide fluid communication between an inner zone defined within the inner wall and the attached growth media zone.